An integrated circuit usually use a conventional radio frequency cascode amplifier as an input or output stage of the integrated circuit. However, the noise figure becomes severe as the gain improved by the conventional radio frequency cascode amplifier.
If the integrated circuit uses an amplifier, without a cascode circuit, as an input or output stage of the integrated circuit, then a gain efficiency of the amplifier may not meet the requirement. Therefore, it may be a difficult decision to make tradeoff between the gain efficiency and the noise figure when determining to use or not to use a cascode amplifier.
Further, a conventional radio frequency amplifier, with or without a cascode circuit, may not be fit in a multiband or wideband device because of the operating frequency of the conventional radio frequency amplifier is limited in a narrow range and not adjustable.
Accordingly, it is imperative to provide a radio frequency amplifier and an integrated circuit using the radio frequency amplifier which can overcome the aforesaid drawbacks of the conventional radio frequency amplifiers.